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At least 829 records · Page 46Linked to original sources
PubMed2005

Human cooperation: second-order free-riding problem solved?

Panchanathan and Boyd describe a model of indirect reciprocity in which mutual aid among cooperators can promote large-scale human cooperation without succumbing to a second-order free-riding problem (whereby individuals receive but do not give aid). However, the model does not include second-order free riders as one of the possible behavioural types. Here I present a simplified version of their model to demonstrate how cooperation unravels if second-round defectors enter the population, and this shows that the free-riding problem remains unsolved.

Cooperative Behavior↗
PubMed2003

Inbreeding depression in fecundity and inbred line extinction in the bulb mite, Rhizoglyphus robini.

This study investigated the magnitude of inbreeding depression in fecundity, and whether the depression is purged during six generations of sib mating in the bulb mite, Rhizoglyphus robini. The progeny resulting from a single generation of brother-sister mating suffered significant inbreeding depression in fecundity. During the following six generations of continuous sib-mating, 58% lines were lost, 45% because of sterility and 13% because of preadult mortality. The lines were then outcrossed, and their inbreeding depression compared with that of the base population. The inbreeding depression for the outcrossed population was 0.15, and for the base population 0.19, but the difference was not significant. The lack of significant purging of inbreeding depression indicates that it was caused either by detrimental genes of small effect, or by the breaking down of overdominant relations between alleles. However, the large proportion of extinct lines points to the former mechanism as a predominant cause of inbreeding depression. Theory predicts that the probability of line extinction with inbreeding increases with its load of mutations. If phenotypic variation in fecundity was partly because of differences in numbers of mutations carried by individuals, the fecundity of the line founder could be expected to correlate with the probability that the line derived from it will survive long-term inbreeding. Indeed, fecundity of founder females was significantly associated with line survival, which suggests that line extinction rate may be used as a method to study individual mutational loads, for example, in studies of sexual selection.

Animals↗
PubMed2006

Exactly solvable approximating models for Rabi Hamiltonian dynamics.

The interaction between an atom and a one mode external driving field is an ubiquitous problem in many branches of physics and is often modeled using the Rabi Hamiltonian. In this paper we present a series of analytically solvable Hamiltonians that approximate the Rabi Hamiltonian and compare our results to the Jaynes-Cummings model which neglects the so-called counter-rotating term in the Rabi Hamiltonian. Through a unitary transformation that diagonalizes the Jaynes-Cummings model, we transform the counter-rotating term into separate terms representing several different physical processes. By keeping only certain terms, we can achieve an excellent approximation to the exact dynamics within specified parameter ranges.

Biophysical Phenomena↗
PubMed2003

Decision analysis as a tool to support an analytical pattern-of-reasoning.

Decision analysis is offered as a tool to aid nurses' decision-making in complex and troublesome situations where there are mutually exclusive actions and time is available for deliberation. Decision analysis can be formal or informal. Formal decision analysis provides a structure for representing the decision situation and a mathematical procedure for prescribing the alternative action that is most consistent with what is known and what one values. Informal decision analysis uses the concepts and sometimes the structure of decision analysis, but usually does not include the mathematical calculations. In the present paper, the authors illustrate how formal and informal decision analysis might be used by nurses to: (i) enhance their own decision-making; (ii) assist patients or family caregivers with decision-making and; (iii) promote informed health care policy development. Finally, the advantages and limitations of decision analysis are discussed.

Caregivers↗
PubMed2005

Transition probabilities of a string oscillator subject to impulsive collisions with a heavy mass point.

Impulsive linear collisions between a string oscillator (a one-dimensional particle in a box) and a mass point are studied quantum mechanically. In the limit of a very heavy mass point (which corresponds classically to many collisions during a single encounter) the transition probabilities are determined exactly. The result permits a discussion of the mixed quantum-classical regime where the collider becomes almost classical while the oscillator remains quantum mechanical. While the average transition probabilities P(m-->n) are well reproduced by the Ehrenfest mean-field approximation, the prediction for the superimposed high-frequency resonance structure is qualitatively wrong for a genuine quantum oscillator. Only if the oscillator is also almost classical and if (m-n)2 square root(mu) << m, where mu is the mass ratio collider/oscillator, this structure is correctly predicted by the Ehrenfest approximation.

Chemistry, Physical↗
PubMed2005

(HCl)2 and (HF)2 in small helium clusters: quantum solvation of hydrogen-bonded dimers.

We present a rigorous theoretical study of the solvation of (HCl)(2) and (HF)(2) by small ((4)He)(n) clusters, with n=1-14 and 30. Pairwise-additive potential-energy surfaces of He(n)(HX)(2) (X=Cl and F) clusters are constructed from highly accurate four-dimensional (rigid monomer) HX-HX and two-dimensional (rigid monomer) He-HX potentials and a one-dimensional He-He potential. The minimum-energy geometries of these clusters, for n=1-6 in the case of (HCl)(2) and n=1-5 for (HF)(2), correspond to the He atoms in a ring perpendicular to and bisecting the HX-HX axis. The quantum-mechanical ground-state energies and vibrationally averaged structures of He(n)(HCl)(2) (n=1-14 and 30) and He(n)(HF)(2) (n=1-10) clusters are calculated exactly using the diffusion Monte Carlo (DMC) method. In addition, the interchange-tunneling splittings of He(n)(HCl)(2) clusters with n=1-14 are determined using the fixed-node DMC approach, which was employed by us previously to calculate the tunneling splittings for He(n)(HF)(2) clusters, n=1-10 [A. Sarsa et al., Phys. Rev. Lett. 88, 123401 (2002)]. The vibrationally averaged structures of He(n)(HX)(2) clusters with n=1-6 for (HCl)(2) and n=1-5 for (HF)(2) have the helium density localized in an effectively one-dimensional ring, or doughnut, perpendicular to and at the midpoint of the HX-HX axis. The rigidity of the solvent ring varies with n and reaches its maximum for the cluster size at which the ring is filled, n=6 and n=5 for (HCl)(2) and (HF)(2), respectively. Once the equatorial ring is full, the helium density spreads along the HX-HX axis, eventually solvating the entire HX dimer. The interchange-tunneling splitting of He(n)(HCl)(2) clusters hardly varies at all over the cluster size range considered, n=1-14, and is virtually identical to that of the free HCl dimer. This absence of the solvent effect is in sharp contrast with our earlier results for He(n)(HF)(2) clusters, which show a approximately 30% reduction of the tunneling splitting for n=4. A tentative explanation for this difference is proposed. The implications of our results for the interchange-tunneling dynamics of (HCl)(2) in helium nanodroplets are discussed.

Chemistry, Physical↗
PubMed2006

Chromophores in phenylenevinylene-based conjugated polymers: role of conformational kinks and chemical defects.

The influence of chemical defects and conformational kinks on the nature of the lowest electronic excitations in phenylenevinylene-based polymers is assessed at the semiempirical quantum-chemical level. The amount of excited-state localization and the amplitude of through-space (Coulomb-like) versus through-bond (charge-transfer-like) interactions have been quantified by comparing the results provided by excitonic and supermolecular models. While excitation delocalization among conjugated segments delineated by the defects occurs in the acceptor configuration, self-confinement on individual chromophores follows from geometric relaxation in the excited-state donor configuration. The extent of excited-state localization is found to be sensitive to both the nature of the defect and the length of the conjugated chains. Implications for resonant energy transfer along conjugated polymer chains are discussed.

Carbon↗
PubMedDate not supplied

Cumulative damage models in cancer epidemiology: application to human incidence and mortality data.

Cumulative damage models are a special class of mathematical models within reliability theory that describe the probability of failure of a given system under the impact of a damaging environment. Though originally introduced to handle wear and tear processes, their concepts can easily be interpreted in terms of the epidemiologic aspects of human carcinogenesis. This paper introduces the new approach and demonstrates its applicability to human cancer incidence and mortality data from Denmark and the Federal Republic of Germany. A slight simplification of the originally stochastic model provides an explicit formula for the relative risk between different populations, which predicts that this basic measure used in cancer epidemiology may have to be considered age-dependent in contrast to a widely used practice which, for convenience, postulates age-independent relative risks. A comparison with empirical data reveals that the concept of age-dependent relative risks is not inconsistent with real world examples of cancer incidence. Thus, some basic assumptions and concepts of epidemiology concerning carcinogenesis and strategies for data analysis may require reconsideration.

Cohort Studies↗
PubMed1975

Sex differences in the comprehension of spatial orientation.

This research examined effects of instruction upon acquisition of Piaget's concept of horizontality and determined sex differences related to this acquisition. Hypotheses tested were that there are no significant differences (a) in performance on perception and prediction tasks, (b) by sex in the ability to comprehend horizontality, (c) by sex in the stage of development after instruction, and (d) by sex after instruction on the number of correct responses on horizontal tasks. Subjects were 18 male and 17 female rural, public school pupils ranging in age from 8 years, 0 months to 9 years, 11 months. Test instruments were a cylindrical bottle half-filled with colored water and eight pictures of bottles positioned at angles from 0 to 315 degrees at increments of 45 degrees. Chi square tests indicated that males performed significantly better than females on perception and prediction, and that instruction significantly improved male performance on prediction and female performance on prediction and perception. It was concluded that females, if given instruction, could more closely approximate the performance of males on the horizontal water level task.

Child↗
PubMed2005

Generation of hypotheses in Wason's 2-4-6 task: an information theory approach.

We explored the "context of discovery" in Wason's 2-4-6 task, focusing on how the first hypothesis is generated. According to Oaksford and Chater (1994a) people generate hypotheses extracting "common features", or regularities, from the available triples, but their model does not explain why some regularities contribute to the hypothesis more than do other regularities. Our conjecture is that some regularities contribute to the hypothesis more than do other regularities because people estimate the amount of information in the perceived regularities and try to preserve as much information as possible in their initial hypotheses. Experiment 1, which used two initial triples, showed that the presence of high-information relational regularities in the initial triples affected the information in the initial hypotheses more than did the presence of low-information object regularities. Experiment 2 extended the results to the classic situation in which only one initial triple is given. It also suggested that amount of information is the only aspect of the structure of the triple that affects hypotheses generation. Experiment 3 confirmed the latter finding: Although relations are commonly distinguished between first-order and higher order relations, the latter being most important for generating hypotheses (Gentner, 1983), higher order relations do have an effect on Wason's 2-4-6 task only if their presence incre ases information. In the conclusion we discuss the statistical soundness of human hypotheses generation processes, and we ask an unanswered question: Amount of information explains why some regularities are preferred to others, but only within a set of "nonarbitrary" regularities; there are object regularities that are rich in information content, but are considered "arbitrary", and are not used in generating hypotheses. Which formal property can distinguish between these two sets of regularities?

Adult↗
PubMed2006

A Quisling on neonatal jaundice.

BACKGROUND/METHODS: Nils Andreas Quisling was born in Telemark, Norway, in 1854 and became an obstetrician. In 1893 he published a monograph on neonatal jaundice. This monograph was studied and compared with other published sources from the same time period. RESULTS: Quisling discussed four theories on the cause of neonatal jaundice. "Suppression jaundice" held that jaundice was the result of suppressed liver function. "Haematogenous jaundice" claimed that bilirubin was formed from haemoglobin outside the liver, and had nothing to do with the liver. "Polycholia" held that neonatal jaundice was due to an increased secretion of all the constituents of bile. Quisling rejected these and supported the "hepatogenous" theory-jaundice was always a liver-related phenomenon. He described 50 cases of neonatal jaundice. The incidence of neonatal jaundice at the Kristiania Maternity Foundation was 26%. In Quisling's cases, gastrointestinal disturbances were common, and he felt this to be an under-reported complication of neonatal jaundice. He found that neonatal jaundice was often accompanied by fever. CONCLUSION: Gastrointestinal disturbances were causally involved in neonatal jaundice, resulting in impeded bile drainage. At the time of Quisling's study (1887), this "hepatogenous" theory of neonatal jaundice probably still had majority support in the European literature.

History, 19th Century↗
PubMed1993

Access to visual information from a name is contingent on access to identity-specific semantic information.

In this study, we investigated subjects' ability to retrieve information about a familiar person's facial appearance in response to seeing their name. Each famous name was associated with one of four occupations (sport, music, politics, and acting) and one of four distinctive facial features (beard, long hair, glasses, baldness). Subjects were asked to state which occupation, and which facial feature was associated with each name. The most important finding was that subjects were generally only able to recall the distinctive facial feature that a person possessed if they were also able to recall their occupation. Recall of the person's occupation, by contrast, was not contingent on remembering the person's facial appearance. These results suggest that there are no direct links between the representation of a person's name in memory and visual information about their facial appearance. The link appears to be indirect, and to be mediated by non-visual semantic information about the person, such as their occupation. This conclusion was also supported by an examination of the effects of biographical cues on subjects' ability to recall facial information that they had previously failed to recall. In a second experiment, subjects were presented with biographical details about famous people, and were asked to retrieve information about their face and name. Retrieval of facial information did not appear to be contingent on recall of the name, nor did recall of the name appear to be contingent on retrieval of facial information. On the basis of the results, an hierarchical model of name recognition is presented which is analogous to current models of face recognition (e.g. Bruce & Young, 1986).

Adult↗
PubMed1994

Involuntary conscious memory and the method of opposition.

Priming in an indirect test of stem completion should reflect involuntary memory, but can be accompanied by conscious awareness of the past (involuntary conscious memory) or unaccompanied by such awareness (involuntary unconscious memory). We adapted the method of opposition developed by Jacoby, Woloshyn, and Kelley (1989) to obtain a measure of stem-completion priming that should reflect only involuntary unconscious memory. Subjects completed stems with the first word coming to mind, but wrote down a different word if the word that came to mind first had been previously encountered. Facilitatory priming was expected only when involuntary unconscious influences outweighed inhibitory effects of involuntary conscious memory, or of intentional retrieval. We observed a facilitation effect for items processed graphemically at encoding, in conjunction with an inhibition effect for items processed semantically at encoding. In contrast, a standard indirect test showed similar levels of priming following graphemic and semantic encoding, whereas a direct test showed a strong advantage of semantic over graphemic encoding. We argue that the two encoding activities produced approximately equivalent involuntary influences of memory, but that items encoded semantically were associated with involuntary conscious memory to a greater extent than were items encoded graphemically. Comparing indirect and opposition test performance can provide a quantitative index of relative levels of involuntary conscious and involuntary unconscious memory.

Analysis of Variance↗